Acid secretion is regulated by a myriad of chemical transmitters delivered to the fundic mucosa by blood and nerves and from local tissue stores. This renewal proposal is based upon the hypothesis these pathways regulating acid secretion interact at multiple points within the fundic mucosa, both at final target cells and modulating delivery of endocrine/paracrine transmitters. The broadest aim of this proposal is to further delineate the factors regulating delivery of these transmitters and the nature and locus of the receptors and cellular mechanisms mediating their effects on both parietal and somatostatin cells. The approach is reductionistic, isolating cells from canine fundic muocsa by enzyme treatment. Cells will be separated by velocity and density cell techniques and identified using a variety of immunohistochemical, endcrine, and biochemical markers. The dual effects of gastrin, to stimulate parietal cells and to cause the release of somatostatin, underline the importance of delineating the interactions between inhibitory and stimulatory pathways. Studies will thus focus on stimulatory elements (gastrin and acetylcholine) and inhibitory elements [thyrotropin releasing hormone (TRH), epidermal growth factor (EGF), and somatostatin]. Radioligand techniques, coupled with autoradiography, will be used localize receptors on mucosal cells for each of these transmitters. Receptor characterization will biological responses to these transmitters, primarily studying parietal cell function (weak base accumulation) and release of somatostatin from cells in short term culture. Mechanisms and cellular elements mediating stimulation and inhibition by these chemical transmitters will be studied, focusing on the role of calcium and protein and receptor phosphorylation. This approach and the potential for understanding the interplay of factors regulating parietal cell function will be greatly enhanced by developing techniques for isolation and characterization of the plasma membrane receptors. The long range goal of this proposal is to understand critical control mechanisms for acid secretion in normal physiology and as they relate to acid hypersecretion in acid peptic disease and influence the response to therapeutic intervention.